A single computer generated image of medium resolution, for example 1024 horizontal by 1024 vertical picture elements (pixels), each having eight bits per red, green and blue color, requires approximately three million bytes (3 MB) of data to express. Transferring such a large data file between data processors, such as workstations, places a significant burden on conventional high-speed serial networks.
Furthermore, performing animated display sequences, which may require realtime display update rates of 30 frames/second or more, is impossible to accomplish with presently available serial interface technologies.
As such, it is desirable to employ a parallel data interface technology so as to increase the bandwidth of the communications bus. One parallel interface technology is described in a specification entitled "High-Performance Parallel Interface Mechanical, Electrical, and Signalling Protocol Specification (HPPI-PH)" preliminary draft proposed, American National Standard for Information Systems, Nov. 1, 1989, X3T9/88-127, X3T9.3/88-032, REV 6.9, the disclosure of which is incorporated by reference herein.
The HPPI interface specifications provides for transfers of 100M bytes/second using a 32-bit port, or 200M bytes/second if a 64-bit port is used. This particular interface technology is thus particularly attractive for use in transferring, by example, digital image animations between workstations.
However, the HPPI interface is intended as a point-to-point, simplex interface between mainframe computers, or between a mainframe and a high-speed disk storage system. The distance between nodes is limited to 25 meters and connections between multiple nodes, so as to provide broadcast or multicast transmissions, is not intended.
It is thus an object of the invention to provide a high speed, high bandwidth parallel communications bus for simultaneously transferring image data from an image server to a plurality of workstations.
It is another object of the invention to provide method and apparatus for use by a plurality of workstations in receiving image data from an image data server and for propagating communication bus control signals to the server.